Heat pumps have the ability to move thermal energy from one environment to another. In general, heat pumps work as follows: the refrigerant, in its gaseous state, is pressurized and circulated through the system by a compressor. On the discharge side of the compressor, the now hot and highly pressurized vapor is cooled in a heat exchanger (preferably a condenser) until it condenses into a high pressure, moderate temperature liquid. The condensed refrigerant then passes through a pressure-lowering device such as an expansion valve. The low pressure, liquid refrigerant leaving the expansion valve enters another heat exchanger (preferably an evaporator), in which the fluid absorbs heat and boils. The refrigerant then returns to the compressor and the cycle is repeated. The evaporator extracts heat from a heat source and the condenser supplies heat to a heat consumer.
In case of geothermal heat pumps, the heat of the ground, groundwater or surface water is used as heat source for in most cases heating buildings. The thermal recharge of the heat source rely on the migration of heat from the surrounding geology and the seasonal temperature cycles at ground level. Two common types can be distinguished, namely open loop systems and closed loop systems.
In an open loop system the natural water from a well (groundwater or surface water) is pumped into an heat-exchanger of the heat pump circuit containing a refrigerant. The specific heat of the water is extracted and the cooled water is returned to a separate injection well, irrigation trench or body of water. The supply and return lines must be placed at sufficient distance from each other to ensure thermal recharge of the water heat source.
A disadvantage of the above open loop system is that, whereas extraction of latent heat would increase the output of the heat source, only specific heat can be extracted. One of the reasons is that ice formed by extraction of latent heat is very difficult being pumped again into the separate injection well, irrigation trench or body of water.
Another disadvantage of open loop systems is the size of the installation because of the high volume of circulating water required and the distance between the supply and return lines.
Further, another disadvantage is that open loop heat pump systems depend on the local legislation with regards of the use of ground and surface waters.
In a closed loop system the heat pump circulates a liquid or a refrigerant through the closed loop tubing in the underground or in a water reservoir to exchange heat.
Although latent heat of the water in the ground can be extracted, a severe limitation however is that the heat flux in the underground is predominantly limited by the thermal conductivity of the ground and the formation of ice-layers sticking around the tubing of the loop.
Another disadvantage of closed loop systems is the size of the ground heat exchangers and the size of the water reservoir because of the required amount of heat stored in the underground or in the water reservoir to supply sufficient heat during the winter period. An example thereof is described in DE440599. The size of the water reservoir is an important restriction to apply the technology in densely populated areas.
In an attempt to enhance the ice melting again thereby reducing the required size of the reservoir, additional heat sources such as solar panels can be added as described in patent EP1807672, which makes recharging the reservoir more complex and expensive.
Another example of ice melting in a closed loop system is described in U.S. Pat. No. 6,681,593, using a shallow pool with heat extractors for extracting latent heat and bristle brush conveyors for removing floating pieces of ice from the pool into the reservoir. Obviously, such system is complex, expensive and the shallow pool occupies additional surface area.
Further, another disadvantage of a closed loop heat pump system is that per definition external waters containing waste heat energy such as domestic waste water cannot be used as heat source to supply latent heat instead of specific heat.
Reference can be made to following patents, DE 2952541 A1, DE10114257 A1, DE 102010006882 A1, DE 202004006853 U1, EP1807672, U.S. Pat. No. 6,904,976 B2, WO2009123458 A1 encountering the disadvantages mentioned above.
Therefore, it is an object of the present invention to provide a heat pump system delivering equal or improved performance compared to known heat pump systems with smaller heat source reservoirs compared to the current heat pump systems.
It is also an object of the present invention to provide a heat pump system having suitable characteristics for use in urbanized areas in particular in areas suffering from lack of building space.
Another object of the present invention is to provide a heat pump system less suffering from heat flux limitation due to ice formation.
Another object of the present invention is to provide a heat pump system allowing less complex and expensive recharge of the heat source, in particular allowing recharging during warm seasons.
Further, another object of the present invention is a heat pump system allowing use of rain water as well as waste heat energy in waste liquids as a heat source, in particular domestic waste water.
In addition, it is an object of the present invention to provide a heat pump system being less independent on the local legislation with regards of the use of ground and surface waters.
In addition, it is an object of the present invention is to provide a heat pump system allowing generation of heat during electrical off-peak hours.
The present invention addressed the above objects by proposing a heat pump system comprising an heat-exchanger extracting latent heat from liquid stored in a reservoir, thereby forming ice slurry, and means for delivering said heat to a heat consumer, characterized in that the heat pump system comprises random input of extrinsic liquid into the reservoir and means removing ice slurry outward the system.